Question 47(b)A gaseous compound of nitrogen and hydrogen contains 12.5% hydrogen by mass. Find the molecular formula of the compound if its relative molecular mass is 37. (N = 14, H = 1).

Question

Accepted Answer

Element% compositionAt. wt.Relative no. of atomsSimplest ratioNitrogen100 - 12.5 = 87.51487.514\dfrac{87.5}{14}1487.5​ = 6.256.256.25\dfrac{6.25}{6.25}6.256.25​ = 1Hydrogen12.5112.51\dfrac{12.5}{1}112.5​ = 12.512.56.25\dfrac{12.5}{6.25}6.2512.5​ = 2Simplest ratio of whole numbers N : H = 1 : 2Hence, empirical formula is NH2Empirical formula weight = 14 + 2(1) = 16Relative molecular mass = 37n=Molecular weightEmpirical formula weight=3716=2.31=2\text{n} = \dfrac{\text{Molecular weight}}{\text{Empirical formula weight}} \[0.5em] = \dfrac{37}{16} = 2.31 = 2n=Empirical formula weightMolecular weight​=1637​=2.31=2∴ Molecular formula = n[E.F.] = 2[NH2] = N2H4

Element	% composition	At. wt.	Relative no. of atoms	Simplest ratio
Nitrogen	100 - 12.5 = 87.5	14	$\dfrac{87.5}{14}$ = 6.25	$\dfrac{6.25}{6.25}$ = 1
Hydrogen	12.5	1	$\dfrac{12.5}{1}$ = 12.5	$\dfrac{12.5}{6.25}$ = 2

Mole Concept & Stoichiometry Miscellaneous Exercises — Question 49

Question 47(b)